A typical AR-15 bolt carrier group relies on precision manufacturing and assembly to ensure the proper flow of gas within the firearm. Any deviation (such as mismatched parts, flaws in mating surfaces, and/or debris introduced during assembly or operation of the firearm) can result in the loss of gas through the firearm.
Some attempts have been made to improve gas sealing in critical areas of the firearm using a painted on sealing media. While somewhat effective, the sealing media is typically painted on by hand, resulting in inconsistent coverage from part to part.